This invention relates to a method of making carbides and nitrides, particularly silicon and metal carbides.
Silicon carbide is a material with high hardness, wear and corrosion resistance, and chemical stability which makes it an excellent material for a wide range of applications. It can, for example, be used in particulate or bonded form as an abrasive or a ceramic.
The production of very fine metal carbides is particularly desirable to produce dense ceramics.
Silicon carbide is produced by reducing silica (silicon dioxide) in the presence of carbon. Normally a stoichiometric excess of carbon is used. One known such method is to heat silica in the presence of coal or coke resulting in a large silicon carbide mass being produced which has to be crushed and milled to an appropriate particle size. This is expensive when fine material is required.
Intimate mixing between the silica and the carbon increases the reactivity and this intimate mixing can be achieved by using a sol-gel process. This process may, for example, involve preparing a precursor such as a colloidal silica-pitch/sucrose system or by the hydrolysis of a methyltrimethoxysilane-phenolic resin/sucrose system. The precursor is pyrolysed in argon producing a sinterable silicon carbide powder.